Electromagnet coil construction



Nov. 5, 1968 H. UHLMANN ETAL 3,409,852

ELECTROMAGNET COIL CONSTRUCTION Filed April 12. 1966 4 Sheets-Sheet 1Nov. 5, 1968 H. UHLMANN ET AL 3,409,852

'EIJECTROMAGNET COIL CONSTRUCTION Filed April 12. 1966 4 Sheets-Shoat 2Fig.5

Nov. 5, 1968 UHLMANN ETAL ELECTROMAGNET COIL CONSTRUCTION 4 Sheets-Sheet4 Filed April 12. 1966 United States Patent 3,409,852 ELECTROMAGNET COILCONSTRUCTION Helmut Uhlmann, Erlangen, and Georg Adam, Berlin, Germany,assignors to Siemens Aktiengesellschaft, Munich, Germany Filed Apr. 12,1966, Ser. No. 542,144 Claims priority, applicatign fiermany, Apr. 17,1965,

11 Claims. 61. 335-216) ABSTRACT OF THE DISCLOSURE Our invention relatesto electromagnets, and especially to electromagnetic coils.

Our invention relates in particular to electromagnet coils capable ofproviding magnetic fields which are not circumferentially symmetrical,such as, for example, longitudinally elongated transverse fields orquadrupole fields. Fields of this type are required for differenttechnical and scientific purposes. Coils of this type are particularlyuseful in those cases where charged particles, such as, for example,ions, electrons and other elementary particles, are to be exposed to atransverse magnetic field, which is to say a magnetic field whichextends perpendicularly with respect to the direction of movement of theparticles. Such coils are therefore particularly required to act asdirection-changing magnets for magnetohydrodynamic generators andparticle accelerators.

In order to achieve longitudinally elongated transverse fields, it isknown to use separate coil sections which form an intermediate spacepassing through the coil. Such coils have a pair of cylindrical windingsof oval cross section. The particles whose direction of movement is tobe changed can enter into the intermediate space between the pair ofcoils into the magnetic field which extends primarily longitudinally ofthe cylinder, and the particles also leave the coil through thisintermediate space. Such coils have the disadvantage of creatingundesirable stray losses resulting from the intermediate space betweenthe windings, and these stray losses result in distortion of the fieldprecisely at that part thereof through which the particles whosedirection is to be changed pass. Therefore, a homogeneous field issituated only in a relatively small region within the coil. Moreover,the field which is available for changing the direction of the particlesis weakened by the field losses which occur in the intermediate space.

It is possible to prevent, in part, the field losses and distortionsresulting from the use of separated coil sections by refraining fromusing, to achieve the transverse magnetic fields, an intermediate spacebetween the windings which passes completely through the coil. It ispossible to use instead a coil having a pair of elongated windingsprovided with longitudinally extending sides which engage each other andwith ends which are curved to a saddle-shaped configuration in such away that the interior of the coil is accessible at the ends of thewindings for the particles whose direction is to be changed. Inasmuch asthe ends of the windings are curved with a coil of this type, theindividual windings of the coil are no longer situated in a singleplane.

With a coil whose windings have this type of saddle- "ice shapedcurvature at their ends there is, however, the difliculty of forming thecoil in such a way that a high winding density, and therefore a smallwire consumption is achieved, and there is in addition the problem ofmaking it possible to manufacture such coils with winding machines. Ifthe coil windings initially have an oval, flat form and then are curvedupwardly, then during the upward bending the individual wires of thecoil shift one with respect to the other. As a result only a relativelylow wire density, or filling factor, is achieved. When the winding iscarried out by machine on a Winding body, the windings can only bemounted in a relatively loose form, since otherwise the bending of thewound coil body is not possible.

Similar difliculties are encountered with magnet coils having more thantwo windings for achieving magnetic fields which are notcircumferentially symmetrical, such as, for example, quadrupole fields.

It is a primary object of our invention to provide an electromagnet coilhaving elongated windings which have longitudinally extending sideswhich are parallel to each other and which have ends curved to asaddle-shaped configuration, while avoiding all of the above problems.

A further object of our invention is to provide for winding layers ofthe coil a layer-receiving means which enables the coil to becontinuously wound with wire which is maintained under tension duringthe winding of the layers and with the winding being carried out in sucha way that lateral slipping of the wire during winding thereof isprevented.

It is therefore an object of our invention to provide a magnet coilwhich is made up of a particularly dense, strong assemblage of windingshaving a high filling factor.

Furthermore, it is an object of the invention to provide for the coilits final configuration during its manufacture, so that bending of thecoil after manufacture thereof is unnecessary and thus shifting of thewires one with respect to the other is avoided.

It is a particular object of our invention to provide an electromagnetcoil composed of superconductive wire. It is especially whensuperconductive wire is used that a dense strong construction of thecoil is required so that with the smallest possible length of wire thegreatest possible magnetic field can be achieved.

Furthermore, the objects of our invention include the provision of acoil which can be manufactured with a conventional winding machine.

Our invention also includes the provision of a layerreceiving meanswhich is capable of absorbing the forces which act on the coil windingsand which result from the magnetic field encountered during operation ofthe coil. Particularly with superconductive coils these forces areespecially great becauset of the strong magnetic field.

The electromagnet of our invention has an elongated coil provided withlongitudinally extending parallel sides and curved ends of saddle-shapedconfiguration, with the coil composed of a plurality of winding layerslocated one adjacent the other with the windings of any one layer allhaving the same length and with the portions of the windings whichextend along the sides of any one layer all being located in a commonplane. The coil of our invention further include-s a layer-receivingmeans defining a groove which receives the winding layers and which haselongated parallel sides and saddle-shaped ends conforming to theconfiguration of the winding layers.

Our invention is illustrated by way of example in the accompanyingdrawings which form part of this application and in which:

FIG.1 is a schematic perspective illustration of one winding layer of acoil of our invention;

FIG. 2 is a perspective illustration of a pair of layerreceiving meansof our invention joined together to form an electromagnet coil;

FIG. 3 is a perspective illustration of a special embodiment of alayer-receiving means of our invention;

FIG. 4 is a fragmentary perspective illustration of the layer-receivingmeans of FIG. 3, the section of FIG. 4 being taken in a plane whichextends perpendicularly with respect to the longitudinal sides of thecoil;

FIG. 5 is a fragmentary perspective illustration of another embodimentof a layer-receiving means of our invention, the section of FIG. 5 alsobeing taken in a plane which extends perpendicularly across thelongitudinally extending sides of the coil;

FIG. 6 is a fragmentary perspective illustration of the winding layers,the section of FIG. 6 also being taken in a plane which extendstransversely across the longitudinal sides of the coil and FIG. 6schematically show ing the electrical connections for the coil;

FIG. 7 is a perspective illustration of a further embodiment of a coilaccording to our invention;

FIG. 8 is a fragmentary perspective illustration of yet anotherembodiment of a layer-receiving means of our invention, the section ofFIG. 8 being taken in a plane which extends perpendicularly across thelongitudinal sides of the coil; and

FIG. 9 is a fragmentary perspective illustration of yet anotherembodiment of a layer-receiving means of our invention, the section ofFIG. 9 also being taken in a plane which extends perpendicularly acrossthe sides of the coil.

The configuration of a winding layer of the electromagnet coil of ourinvention can best be understood by visualizing an endless band ofuniform width having opposed edges of uniform length, this bandinitially having the configuration of a cylinder and then being deformedin such a way that a pair of opposed portions of the band are turnedinto a common plane with the edges of the band portions which are in thecommon plane extending parallel to each other, so that the innersurfaces of the two turned band portions are situated on the same sideof the plane. An endless band of the above construction which has beentreated in the above manner is illustrated in FIG. 1 which shows thepair of turned elongated band portions 1 and 2 which form thelongitudinally extending sides of the coil, these band portions 1 and 2extending parallel to each other in a common plane. As a result of thisdeformation of the initially cylindrical endless band, the end portions3 and 4 of the band, which form the ends of the coil, have thesaddle-shaped curvature shown in FIG. 1. This band which is of uniformwidth is a model for a winding layer of the coil, this layer beingcomposed of wire windings situated one next to the other. Inasmuch asthe band in its initial cylindrical form has edges of uniform length, itfollows that all lines drawn on the band parallel to the edges thereofare necessarily of the same length. Therefore, the individual wirewindings which conform to the configuration of the band edges and thuscorrespond to such lines necessarily have within the layer of ourinvention equal lengths. By bending the ends to different extents,illustrated by an outward bulging of the upwardly curved band ends, itis possible to vary the configuration of the coil.

By combining additional layers of a configuration similar to that ofFIG. 1 with the layer illustrated therein, all of the winding layers ofthe coil will result. All of the winding layers are oriented in the sameway so that one layer extends along and is located adjacent the other.The configuration of the coil is described in greater detail inconnect-ion with the description of the layer-receiving means below.While the lengths of the individual windings of any one layer are equal,the winding lengths increase from one layer to the next.

In order to provide elongated transverse fields, the electromagnet coilof our invent-ion is made up of two or more coil sections each having apair of elongated sides, and these coil sections are arranged with theirlongitudinally extending sides engaging each other. FIG. 2 shows a pairof layer-receiving means 21 and 22 which are connected together to forma coil according to our invention, the winding layers being omitted fromFIG. 2 so as to show more clearly the details of the pair ofinterconnected layer-receiving means 21 and 22. Each of theselayer-receiving means has a pair of longitudinally extending sides whichare parallel to each other and a pair of saddle-shaped opposed endscurved as illustrated in FIG. 2. The interior space of the coil of ourinvention is, because of the curvature of the ends, accessible from theexterior in a direction which extends perpendicularly with respect tothe magnetic field produced by the structure. Each of thelayer-receiving means 21 and 22 defines a groove which serves to receivethe winding layers. The groove of the layer-receiving means 22 isdescribed below, and of course, the layer-receiving means 21 is formedwith an identical groove which is directed toward the groove of thelayer-receiving means 22. Thus, the layer-receiving means 22 has aninner base surface 23 which defines the base of the layer-receivinggroove and which has a configuration conforming to that of the band ofFIG. 1. Thus, the configuration of the base of the groove matches theconfiguration of the first winding layer. The layer-receiving means 22has a pairof side walls 24 and 25 which extend perpendicularly withrespect to the base surface 23 along the entire length thereof, and itis these side walls 24 and 25 which have the inner side surfaces of thelayer receiving means 22 which define the opposed side surfaces of thelayer-receiving groove. As was mentioned above, the groove of thelayerreceiving means 21 is of the same configuration.

During manufacture of the coil, the individual winding layers are woundwithin the groove in such a way that the individual windings in any onelayer all have the same length. At the junctions 26 between the curvedend portions and elongated side portions of the layer-receiving means22, the side walls 24 and 25 thereof bulge outwardly, thus providing awidening of the coil body. As a result the individual winding layers ofthe coil each have their individual windings of equal length situatedalong the sides of the coil at a density which is difiierent from theirdensity at the ends of the coil. In order to provide a mechanicallystrong coil under these conditions, it is preferred to include with thelayer-receiving means 21 and 22 suitable intermediate shims or the likeof insulating material which are situated at the ends of the coilbetween the individual layers. As a result there is a small loss ofwinding density. This disadvantage is, however, compensated to a verylarge extent by the relatively simple geometric configuration of thelayer-receiving means. Each layer-receiving means can be manufactured ina relatively easy way. The introduction of the windings can take placein a simple way by using a conventional winding machine.

An outward bulging of the side walls at the junction between the curvedend portions and the longitudinal sides is prevented with the embodimentof our invention which is illustrated in FIGS. 3 and 4. Thelayer-receiving means of this embodiment includes a pair of side walls31 and 32 which have inner surfaces defining the opposed inner sidesurfaces of the groove. These side walls are interconnected by atransverse wall 33 which has an inner surface defining the base surfaceof the groove. With this embodiment the outer side wall 31 and the innerside wall 32 extend perpendicularly with respect to the transverse wall33 only along the elongated sides of the layer-receiving means. At thejunctions between the curved ends of the layer-receiving means and thelongitudinally extending sides thereof, the angle between the outer sidewall 31 and the transverse wall 33 becomes smaller while the anglebetween the inner side wall 32 and the transverse wall 33 becomesgreater. The saddle-shaped ends of the layer-receiving meansrespectively have crests 34, and at this crest 34 the outer side wall 31extends from the transverse wall 33 at an angle of from approximately 30to 35 while the inner side wall 32 extends from the transverse wall 33at the crest of each end at an angle of from approximately 150 to 145.Thus, the total of both of these angles is 180". At the crest of eachsaddle-shaped end, the side walls of the layer receiving means extendsubstantially parallel to that part of the wall 33 which extends alongeach side of the layer-receiving means.

In FIG. 3 the configuration of the inner space defined by the walls 3133is partially indicated in dotted lines. At the ends of thelayer-receiving means, the side walls 31 and 32 have a width which ismore than twice their width along the sides of the layer-receivingmeans. The configuration of the base of the groove corresponds to theconfiguration of the first winding layer of the coil of our invention.

The shape of the coil and thus the configuration of the groove of thelayer-receiving means can be best illustrated by a paper model. Thus, aplurality of endless paper strips all of the same width but each of alength somewhat greater than the next are joined together in acoextensive identically oriented manner with the strip of FIG. 1, thislatter strip forming what corresponds to the first winding layer. Thus,the additional strips will correspond to the additional layers of thecoil. The gluing of the several paper strips one to the other is carriedout in such a way that the edges of the assembled strips will definesurfaces which illustrate the configuration of the surface of the grooveof the layer-receiving means, and along the sides the model of the coilwill have surfaces extending perpendicularly with respect to theelongated side portions of the first band shown in FIG. 1. At the endsof the model the surfaces defined by the edges of the joined strips willform angles on the one hand of from approximately 30 to 35 and on theother hand, of from approximately 150 to 145 with the end portions 3 and4 shown in FIG. 1, these end portions of course corresponding to thebase surface of the groove. Inasmuch as these individual paper stripsrep-resent the different winding layers situated one on the other andconform precisely to the configuration of the groove of thelayer-receiving means, this model provides an accurate representation ofthe structure of the coil and its groove.

As is apparent from the above-described construction of a model whichrepresents the coil of our invention, it is possible with the embodimentof FIGS. 3 and 4 to arrange the individual winding layers directly oneupon the other, so that intermediate layers or shims of insulatingmaterial or the like are not required.

With an electromagnet coil having a pair of layer-receiving means asshown in FIG. 3 joined together with their longitudinal sides engagingeach other and with corresponding windings situated in the grooves ofthe layerreceiving means, the maximum field intensity is situated at thecentral plane of the coil, this central plane being defined by the freeedges of the side walls 31 and 32 at the longitudinal sides thereof. Ofcourse, it is the free edges of one set of side walls, at the sides ofthe layerreceiving means which engage, respectively, the free edges ofthe other pair of side walls of the other layer-receiving means alongthe sides thereof. Deviations above and below this central plane willprovide field changes of approximately one percent. The field changesresulting from deviations from the longitudinal axis of the coil withinthe central plane thereof are On the order of 2%. Because of these smalldeviations, it is possible to achieve with the coil of our inventionmagnetic fields having a high degree of homogeneity.

With magnetic fields which have their maximum intensity not in thecentral plane between the pair of coil sections, but above or below thiscentral plane, it is possible to provide a coil according to ourinvention having windings which in cross section are provided along thesides of the coil not with the configuration of a rectangle but ratherwith the configuration of a rhombus. Thus, the groove of alayer-receiving means which serves to receive the winding layers of sucha coil has a corresponding configuration.

FIG. 5 shows such a layer-receiving means, and it will be seen that thegroove of the layer-receiving means of FIG. 5 has indeed theconfiguration of a rhombus in cross section. Thus, along thelongitudinally extending sides of the layer-receiving means, the outerwall 51 extends from the transverse wall 52 at an angle of approximatelyand the inner wall 53 extends from the trans verse wall at an angle ofapproximately 60. At the crest 54 of each curved end portion, the outerwall 51 extends from the transverse wall 52 at an angle which rangesfrom approximately 40 to 45, and the inner wall 53 extends at the crestof each curved end portion from the transverse wall 52 at an angleranging approximately from 140 to Thus, these angles also total 180. Theprecise con figuration of the groove can be demonstrated by a model madeup of paper strips in the same way as described above in connection withFIG. 3. The strips are glued one to the other in such a way that theedges thereof conform to the surfaces which define the sides of thegroove, while the base of the groove conforms to the con-figuration ofthe first strip. With such a model it will be found that the aboveangles are indeed provided. At the crests of the curved ends, the innerand outer side walls of the layer-receiving means extend approximatelyparallel to the transverse wall 52 at its portions which extend alongthe sides of the layer-receiving means.

With a. coil which is composed of a pair of layer-receiving means asshown in FIG. 5 connected one to the other with the free edges of theside walls of one layerreceiving means engaging the free edges of theside walls of the other layer-receiving means, along the sides of thecoils, it has been found that with the winding layers situated in thelayer-receiving means and with the coil in operation, the magnetic fieldwill initially increase in intensity proceeding from the central plane,to an extent of approximately 25%, and then the intensity will decrease.

The angles between the base surface of the groove and the side surfacesthereof at the ends of the layerreceiving means of our invention canhave different values, provided only that the windings received withinthe layerreceiving means all have the same length in any one layer,which is to say the configuration of the winding layer and the form ofthe groove correspond to the models referred to above and made from thejoining together of the endless paper strips which define at their edgesthe surfaces corresponding to those of the groove. Of course, eachendless paper strip has opposed edges of the same length, as pointed outabove. The particular angles referred to above, namely the angles offrom 30 to 35 on the one hand, and 150 to 145, on the other hand, aswell as the angle of from 40 to 45, one the one hand, and to 135", onethe other hand, have, however, proved to be very satisfactory since atthese angles the windings of each layer can have a relatively shortlength. Thus, this feature is of significance with respect to saving ofwire of the coil.

FIG. 6 fragmentarily illustrates the winding layers of a coil of ourinvention without the layer-receiving means. The coil is composed ofseveral winding layers 61 which are formed in such a way that theindividual winding 62 within any one layer all have the same length. Atone of the longitudinal sides of the coil, the wire ends 63 of the coilextend outwardly and are connected with a source of current 64. Theswitch 65 serves to connect the source of current 64 into the circuit orto open the circuit. When the coil is composed of superconductive wire,there is an additional superconductive switch 66 for closing thesuperconducting circuit during superconductive operation.

It is also possible in accordance with our invention to provide alayer-receiving means which does not receive r the entire Windinglayers, so that this layer-receiving means does not form a singleendless groove. In many cases it is suflicient if the layer-receivingmeans only partially receives the winding layers, particularly at thecurved end portions which are difiicult to shape. With a construction ofthis type, the portions of the sides of the winding layers which extendbetween the sections of the layer-receiving means can be rigidly heldtogether by pouring a mass about these portions of the winding layers ina suitable mold in which the mass solidifies so that thereafter theportions of the winding layers which extend beyond and between thesections of the layer-receiving means will remain rigid.

A coil of our invention which includes such a layerreceiving means isillustrated in FIG. 7 where the layerreceiving means is composed of apair of sections 71 and 72 which are separate and spaced from each otherand which respectively receive the saddle-shaped ends 74 and 73 of thewinding layers. The longitudinal side portion 75 of the winding layersextend freely beyond the sections 71 and 72 of the layer-receivingmeans. The ends 76 of the coil are directed outwardly to the side, asschematically indicated in FIG. 7.

When using superconductive wire for the windings of the coil, it is ofadvantage to give the layer-receiving means an exceedingly strongconstruction so that it will be able to absorb the mechanical forcesencountered as a result of the exceedingly intense magnetic fields ofsuperconductive coils. The layer-receiving means need not have in thiscase the rail-like configuration, as has been chosen for illustration inFIGS. 2-5 for the sake of greater clarity. In this case it is preferredto make the layerreceiving means in the form of a massive metal memberformed with a groove only for the purpose of receiving the windinglayers and having in the longitudinal direction of the coil an elongatedspace provided for the particles which are introduced into the magneticfield. Thus, other portions of such a massive body remain as supportmaterial to provide mechanical strengthening of the layerreceivingmeans. It is of particular advantage to use reinforcing ribs with such aconstruction. Where the coil is composed of a plurality of coilsections, the plurality of layer-receiving means can be connected toeach other by screws.

FIGS. 8 and 9 show a pair of layer-receiving means having thesefeatures. The layer-receiving means 81 of FIG. 8 is provided between itsportions which are formed with the groove 82, which receives the windinglayers, with a bridging wall '83 which considerably strengthens thestructure and which defines part of an elongated passage or canal 84over which the bridging wall 83 extends and in which the magnetic fieldis situated. The outer wall of the layer-receiving means 81, whichdefines the outer surface of the groove 82, is fixed with lugs 85 whichserve, in connection with suitable bolts, nuts and the like to fix thelayer receiving means of FIG. 8 with another layer-receiving meansproviding an arrangement such as that shown in FIG. 2, for example.

With the layer-receiving means 91 of FIG. 9, there is in addition to thebridging wall 92 between the sides of the groove 93 a reinforcing rib 94which extends integrally from the bridging wall 92 as well as [from thetransverse wall which defines the base of the groove 93. The passage 95is provided for the magnetic field.

For the manufacture of the layer-receiving means of the invention it isdesirable to use strong metal which can be readily worked. For example,the layer-receiving means in its final form can be derived from analuminum casting. Also, it is possible to manufacture thelayer-receiving means from copper into which is milled the groove forreceiving the winding layers. The use of a material of good heatconductivity, such as aluminum of copper, for the layer-receiving meanswill facilitate cooling of the coil, particularly when superconductivecoils are used. In order to improve the cooling the groove-defining sidewalls may be formed with additional openings which permit the entranceof a cooling medium to the coil windings. Because of the good electricalconductivity of materials such as copper and aluminum, thelayer-receiving means formed from these metals can simultaneously servewith supercodu-ctive coils as shortcircuiting rings to prevent damagingof the coil during the transition between the superconducting and thenormal conducting states.

As superconductive Wire for the coil it is possible to use, for example,niobium-zirconium wi-re. When using cables made up of severalniobium-zirconium wire filaments housed within a plastic sleeve orenvelope, the winding process is considerably simplified. It is alsopossible to use, for example, wires, bands or cables made of niobium-tin(Nb Sn), or layers of niobium-tin can be used. In the event that suchniobium-tin superconductors are to be shaped after the manufacture ofthe coil at temperatures of from approximately 950 to 1000 C., thelayer-receiving means cannot be made of aluminum, inasmuch as thismaterial has a melting point which is too low, and in this case copperwill be used for the layerreceiving means.

During operation in the superconducting state, the entire coil issituated in a cryostat in order to achieve the required lowtemperatures.

The magnet coils of our invention have many uses. The magnet coil formedfrom two or more coil sections, according to our invention, whichachieve a magnetic field whose maximum intensity is situated in thecentral plane of the coil, are particularly suitable for use withmagnetohydrodynamic generators. Where the coil is composed of two ormore coil sections having their maximum field intensity beyond thecentral plane of the coil, the coil is suitable for use as a guidingmagnet for the particle accelerator since the particles whose directionis to be changed often do not pass with such devices through the centralplane of the coil.

As was mentioned above, the winding layers of the coil of our inventioncan be wound on conventional winding machines in which the wire ismaintained under tension. Because all of the windings which in any onelayer are of the same length are wound in a position where the pressurederived from a wire during its winding is always directedperpendicularly against the support beneath the wire, a lateral shiftingof the wire during the winding of the layers is prevented.

The configuration of the cross section of the groove in thelayer-receiving means of the coil of our invention will depend upon theform of the magnetic field which is to be achieved with the coil. Thus,in those cases where the magnetic field is to have its greatestintensity in the central plane between the pair of coil sections, theside surfaces of the groove will have along the sides of the coil anangle of with respect to the base surface thereof. This angle can bemaintained throughout the entire length of the groove or it may varyalong the length of the groove, as pointed out above. The depth of thegroove, which is to say the width of the side surfaces thereof, isselected in such a way that all of the winding layers will be receivedtherein.

We claim:

1. In an electromagnet, a coil comprising a plurality of winding layerslocated one adjacent the other with a plurality of windings forming eachlayer, all of the windings of any one layer being of the same length andeach layer having a pair of elongated parallel sides and a pair ofopposed ends respectively curved from said sides and having asaddle-shaped configuration, the winding portions which form the sidesof any one layer all being located in a common plane, and alayer-receiving means defining a groove receiving said layers at leastin part, said groove having saddle-shaped ends respectively receivingsaid ends of said layers and elongated sides respectively receiving saidsides of said layers, and said layer-receiving means having an innerbase surface of uniform width defining the base of said groove and apair of opposed inner surfaces defining the sides of said groove andterminating in free edges which are located in a common plane along thesides of said groove.

2. A coil as recited in claim 1 and wherein said inner side surfacesextend perpendicularly with respect to said base surface.

3. A coil as recited in claim 1 and wherein said layerreceiving meanshas a pair of opposed groove walls respectively provided with said innerside surfaces of said groove, one of said groove walls being an outerwall and the other of said groove walls being an inner wall and saidwalls extending perpendicularly with respect to said base surface alongthe sides of said groove, said groove walls respectively having crestsat each of the saddleshaped ends of said groove and said outer wallextending at each crest at an angle of less than 90 from the basesurface of said groove while said inner wall extends at each crest fromthe base surface of the groove at an angle which when added to saidangle of less than 90 totals 180.

4. A coil as recited in claim 3 and wherein said angle of less than 90ranges approximately from 30 to 35 while said angle at which said innerwall extends from said base surface at each crest ranges approximatelyfrom 150 to 145.

5. A coil as recited in claim 1 and wherein said sides of said groovehave in cross section the configuration of a rhombus, saidlayer-receiving means having outer and inner side walls respectivelyprovided with said inner side surfaces of said groove and said sidewalls respectively having crests at each saddle-shaped end of saidgroove, said outer wall extending from said base surface of said grooveat each crest at an angle of less than 90 and said inner wall extendingfrom said base surface of said groove at each crest at an angle whichwhen added to said angle of less than 90 total 180.

6. A coil as recited in claim 5 and wherein said outer wall extends atthe sides of said groove from said base surface thereof at an angle ofapproximately 120 while said inner wall extends from said base surfaceof said groove along the sides thereof at an angle of approximately 60,and said angle of less than 90 ranging approximately from 40 to 45 whilesaid angle which, when added to said angle of less than totals 180,range approximately from 140 to 7. A coil as recited in claim 1 andwherein said layerreceiving means includes a pair of spaced bodiesrespectively receiving said ends of said layers and said sides of saidlayers having portions which extend between said bodies.

8. A coil as recited in claim 1 and wherein said layerreceiving means isin the form of an aluminum casting.

9. A coil as recited in claim 1 and wherein said layerreceiving means isin the form of a copper body in which said groove is formed.

10. In an electromagnet, a coil comprising a plurality of winding layerslocated one adjacent the other with a plurality of windings forming eachlayer, all of the windings of any one layer being of the same length andeach layer having a pair of elongated parallel sides and a pair ofopposed ends respectively curved from said side and having asaddle-shaped configuration, the winding portions which form the sidesof any one layer all being located in a common plane, and alayer-receiving means defining a groove which receives said layers, saidlayer-receiving means having an inner base surface defining the base ofsaid groove and a pair of opposed inner side surfaces defining the sidesof said groove, and said layer-receiving means having an outer wallprovided with one of said inner surfaces, an inner wall provided withthe other of said inner side surfaces, and a bridging wall extendingacross the space between and interconnecting those portions of saidinner wall which extend along the sides of said groove.

11. A coil as recited in claim 10 and wherein said layer-receiving meanshas at least one exterior rib projecting from said bridging wall.

References Cited UNITED STATES PATENTS 3,215,871 ll/l965 Brill 310113,270,304 8/1966 Hoppie 335216 3,283,276 11/1966 Hritfay 335299 XRBERNARD A. GILHEANY, Primary Examiner.

GEORGE HARRIS, Assistant Examiner.

